Conventional compression springs are used in a variety of applications. By way of example, FIG. 1 shows one such application of a conventional compression spring 12 employed in a Detroit Locker® differential 10. In this type of application, the conventional compression spring 12 operates to bias the differential into an engaged or disengaged configuration.
FIG. 2 shows a cross-sectional view of another conventional compression spring 50 that takes the form of a round-wire helical compression spring wound about a longitudinal axis 52. The round-wire includes a wire diameter 54 formed about a mean spring diameter 56 with the various coils separated according to a desired pitch 55. In addition, the conventional compression spring 50 includes oppositely facing end surfaces 58, 60 formed on respective end portions 62, 64. The oppositely facing end surfaces 58, 60 may be ground or machined to be substantially planar or flat such that the end surfaces 58, 60 of the spring 50 may be aligned and seated against a substantially planar or complementary surface. For example and briefly referring back to FIG. 1, the oppositely facing end portions 58, 60 of the conventional compression spring 12 are seated, supported, or otherwise in contact with a substantially planar mating surfaces 14, 16. In many industries it is considered a common manufacturing practice to grind or machine down the oppositely facing end surfaces of a compression spring to enable the spring to be seated against a substantially planar surface.
Nevertheless and again referring back to FIG. 2, inner facing surfaces 66, 68 remain round or non-machined. In at least some types of compression springs and/or under certain loads, the inner facing surfaces 66, 68 may contact the adjacent coil under compression. With the rounded spring wire, the upper contacting coil may want to roll off the lower contacting coil and in some cases may become caught or locked beneath a lower contacting coil. In addition, the contact may operate as a stress concentration point on the adjacent coil eventually damaging or even causing failure of the compression spring. Further, this contact may operate as a rocker or hard point to change the stress/strain distribution within the coils of the spring, which in turn may adversely affect various loading conditions and may affect the operational life of the spring.